Compact half-wave balun using microstrip and lumped-element artificial transmission lines

In this paper, a compact two-section half-wave balun using artificial transmission lines is presented. The developed balun comprises four sections of artificial transmission lines, including two sections realized with lumped chip capacitors and via holes. The theoretical performance of the proposed balun is verified through circuit simulations and measurements of a fabricated prototype at 0.9 GHz. The proposed balun exhibits excellent return loss, insertion losses and phase characteristics over the operational frequency band. The measured return loss of input port remain above 11dB over a bandwidth from 0.8 GHz to 1 GHz, while in this frequency range the amplitude imbalance varies from -0.48 dB to 0.37 dB, and the phase difference of 177° to 180°. Measurements show a good agreement with the corresponding simulations.